GB2342205A

GB2342205A - An ambient condition detector with variable sample rate responsive to a non-threshold based profile

Info

Publication number: GB2342205A
Application number: GB9923181A
Authority: GB
Inventors: Lee D Tice
Original assignee: Pittway Corp
Current assignee: Pittway Corp
Priority date: 1998-10-01
Filing date: 1999-09-30
Publication date: 2000-04-05
Anticipated expiration: 2019-09-30
Also published as: CN1250200A; JP2000113343A; GB9923181D0; DE19946980A1; US6222456B1; GB2342205B; CN1227629C

Abstract

A detector includes an ambient condition sensor (40). Outputs from the sensor are sampled at a predetermined rate when the outputs do not represent an alarm condition. The outputs are analysed using pattern recognition techniques to determine if a predetermined non-threshold based profile, which precedes the presence of an alarm condition, is present. In the event that the profile is detected, the sample rate is increased along with associated sample processing. The detector includes a programmable processor (50) coupled to the sensor. The processor includes pattern recognition instructions for detecting the presence of the predetermined profile, and also includes instructions for altering the sample rate in response to the detected presence of the profile. A second sensor, sensing a second ambient condition, may be incorporated, whereby the sampling rate of each sensor is modified in response to the output from the other sensor.

Description

2342205 DETECTOR VVrM VARLABLE SAMEPLE RA

Field of the Invention:

The invention pertains to ambient condition detectors. More particularly, the invention pertains to photoelectric-type smoke detectors with variable sample rates.

Backgj:ound of the Invention:

Smoke detectors have been extensively used to provide warnings of potential or actual fire conditions in a region being monitored. Photoelectric-type smoke detectors sample the contents of a smoke chamber intermittently.

Known photoelectric detectors sample the smoke chamber at a first rate in a quiescent state. In the event that a smoke sample exceeds a preset threshold, the sample rate is increased. If the level of smoke exceeds a threshold for several additional samples, an alarm condition will be indicated.

While known detectors do provide a variable sample rate, it is only in response to the presence of a predetermined smoke density. It would be desirable to be able to vary the rate even for low levels of smoke density without requiring the excessive power that can be required to operate continuously at a relatively high sample rate. Preferably such added functionality could be achieved without any significant increase in either cost or manufacturing complexity.

Suingnga of the Invention:

A detector samples an ambient condition at a predetermined rate.

Circuitry in the detector analyzes the sampled values as they are being received.

If the values meet a predetermined profile, such as a profile of a developing fire, the sampling rate is increased.

In one aspect, the circuitry recognizes the presence of a predetermined profile based on processing samples from an ambient condition sensor. For example, if three amplitude values in-a row consecutively increase, the sample rate can be increased. If four sampled amplitudes in a row consecutively increase, the sample rate can again be increased.

Recognizing a pre-established profile and increasing the sample rate in response thereto provides additional benefits. Other processing such as smoodiing of the sampled values to eliminate uncorreIated noise or carrying out other forms of preliminary processing will be accelerated due to the increased sample rate.

Yet another benefit of the present apparatus and process is that the average power consumption of the respective detector is only increased when the likelihood of a condition to be detected has increased. In systems having large numbers of detectors, the ability to reduce average power or current is particularly advantageous.

In yet another aspect, other recognizable profiles which can be used to produce increased sample rates include increased gradient values of the sampled amplitudes or the value of an integral of the sampled amplitudes. An alternate way in which a sample rate modifying profile can be established is to incorporate a second, different sensor into the detector.

The output signal from the second sensor can be processed. If a selected profile is recognized, the sample rate of the primary sensor can be increased.

Hence, where a selected profile has been recognized, the sample rate will be increased. If the profile is no longer being recognized, perhaps due to changing ambient conditions, the sample rate can be returned to its quiescent value.

As a result, average power consumption will be reduced.

In yet another aspect, a detector can include multiple sensors. These multiple sensors can include a fire sensor or a non-fire sensor as a second sensor.

In the case of more than one fire sensor, the sampling rate would increase if more than one fire sensor is giving an indication of a fire condition. In the case of the non-fire sensor, the sampling rate of the fire sensor would not increase or would decrease if the non-fire sensor is giving an indication of a non-fire condition.

A particular detector could include, a photo-electric, optical, type sensor and an ionization sensor. These are normally sampled at a 5 second rate.

Methods of implementing variable sampling for this example are:

a. if either sensor senses a potential fire condition, then the sampling interval of both the optical sensor and the ionization sensor will be decreased to 2.5 seconds; or b. if the optical sensor senses a potential fire condition, the sampling interval of the ionization sensor will be decreased to 2.5 seconds. This reverse situation results in decreasing the sampling interval of the optical sensor; or C. if both sensors sense a fire condition, then the sampling interval of both sensors will be decreased to 2 seconds (Otherwise, the sampling intervals are unchanged); or d. if neither sensor senses a potential fire condition, then the sampling interval will be increased to 7.5 seconds.

Alternately, the sampling rate could increase linearly with the level of indication of the sensed condition. For example the sample interval could be shortened from a 5 second interval, with no indication, to a 4 second interval with a mild indication, to a 3 second interval with a stronger indication. Finally, the interval can be reduced to a 2 second interval with a very strong indication.

The rate is alterable by downloading different values into the detectors from a common control unit. The common control unit may determine that other devices are sensing a condition and set the remainder of the system or certain other devices to increase their sampling rate.

In yet another aspect, where the sampled signal is processed or filtered, both the sampling rate and the processing can be altered in response to a recognized fire profile. For example, where a predetermined profile has been recognized:

a) the sampling rate can be increased, (and the interval decreased) and the type of filtering changed or the degree of filtering decreased -- both pronliote a faster response; or b) the sampling rate can be increased - to promote a faster response - without altering the type or degree of filtering - thereby providing more information and a greater discrimination of a developing ambient condition; or C) where there are two sensors, if one sensor is responsive to nuisance or false alarm causing conditions, the sampling rate of both sensors could be increased along with increasing the filtering of one or both sensor outputs to minimize false alarms.

Numerous other advantages and features of the present invention win become readily apparent from the following detailed description of the invention and the embodiments thereof, from the claims and from the accompanying drawings.

Brief Description of the Drmugs:

Fig. 1 is a block diagram of a system in accordance with the present invention; Fig. 2 is a block diagram of an ambient condition detector useable with the system of Fig. 1; Fig. 3 is a graph illustrating processing of signals from a detector of the type illustrated in Fig. 2.

Fig. 4 is a block diagram of an alternate form of the detector usable with the system of Fig. 1; Fig. 5A illustrates raw sensor output and a filtered output corresponding thereto plotted as a function of time; Fig. 5B illustrates the effects of increasing the sample rate using the same degree of filtering as was the case of the graph of Fig. 5A; and Fig. 5C illustrates the effects of combining increased sample rate with additional processing to provide a higher degree of fire discrimination than is the case with the response of Fig. 5A but in the same time interval.

DescriVtion of the, 1!referred Embodiments:

While this invention is susceptible of qabodiment in many different forms, there are shown in the drawing and will be described herein in detail specific embodiments thereof with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the specific embodiments illustrated.

Fig. 1 illustrates a system 10 which can be used for monitoring a plurality of conditions in one or more regions to be supervised. The system 10 includes a common control unit 12 which could be implemented as one or more interconnected programmed processors and associated, prestored instructions.

The unit 12 includes an interface for coupling, for example, to a communications medium 14, illustrated in Fig. 1 for exemplary purposes only as an optical or electrical cable. Alternately, the system 10 can communicate wirelessly, such as by RF or infrared, via transceiver 16, illustrated in phantom in Fig. 1, and antenna 16a.

Coupled to medium 14 is a plurality of ambient condition detectors 18 and a plurality of control or function units 20. It will be understood that the relative arrangement of the members of the pluralities 18 and 20 relative to the medium 14 is not a limitation of the present invention. The members of the plurality 18 can include intrusion sensors, position sensors, gas sensors, fire sensors such as smoke sensors, thermal sensors or the like, and gas sensors, all without limitation. The members of the plurality 20 can include solenoid actuated control or function implementing units, display devices, printers or the like.

Where system 10 incorporates a wireless communications medium, a plurality 22 of wireless units could be in bidirectional communication with transceiver 16. The plurality 22 can include, without limitation, ambient condition detectors, as noted above as well as control or furiction implementation devices without limitation.

Also coupled to the control unit 12 via a medium 24, illustrated for example as a pair of electrical cables, is a plurality 26 of output devices. These could include audible or visible output devices without limitation, speech output devices and the like. The devices 26 are intended to broadcast a message, which might indicate alarm condition, in one or more predetermined regions.

Fig. 2 illustrates in block diagram form an exemplary member 18n of the plurality 18. The member 18n, an ambient condition detector, includes an ambient condition sensor 40.

The sensor 40 can include without limitation a smoke sensor such as a photo electric sensor, ionization sensor, gas sensor, humidity sensor or the like. Output from the sensor 40, on a line 40a is coupled to profile detection circuitry 42.

In a quiescent operating state, the sensor 40 can be intermittently energized at a quiescent rate to provide a sampled output on the line 40a.

Alternately, signals on the line 40a can be sampled at the quiescent rate.

Profile detection circuitry 42 is a intended to analyze the output from sensor 40, line 40a, to establish the presence of a possible alarm condition (for example, a possible fire condition or a possible hazardous gas condition) even before a preset threshold, such as a pre-alarm condition, is crossed. When an appropriate profile has been detected by circuitry 42, sampling rate determination circuitry 46, coupled to profile detection circuitry 42, alters, by increasing, the sampling rate of the signal on the line 41a. The sampling rate thus goes from the quiescent rate to a predetermined higher rate.

Altering of the sampling rate can be achieved by incorporating into circuitry 46 analog circuitry such as voltage controlled oscillators or digital circuitry such as counters and the like all without departing from the spirit and scope of the present invention. It will also be understood that other forms of sampling rate altering circuitry also fall within the scope of the present invention.

Circuitry 46 can intermittently energize sensor 40 or it can provide gating signals to the signal on the line 40a, all without departing from the spirit and scope of the present invention.

By means of circuitry 46, since the sampling rate of signals from sensor 40 can be increased in response to the detection of a potential alarm condition, response of the detector l8n to the ambient condition being sensed will be speeded up. In addition, average power requireo'for the detector 18n will be reduced since in the absence of a detected profile, detector l8n operates at a lower sampling rate, thus conserving energy.

Profile detection circuitry and sampling rate determination circuitry 42, 46 are coupled to local control circuitry 48. Control circuitry 48 can in turn control the operation of signal processing circuitry 50 which can provide various types of pre-processing or filtering of signals from sensor 40 prior to coupling those signals via interface circuitry 52 to either medium 14 or wireless transceiver 52a.

It will further be understood that processing circuits 50 can be implemented wholly or in part in detector l8n as well as wholly or in part in common control unit 12 without departing from the spirit and scope of the present invention. One form of pre-processing is disclosed in Tice et al U.S. Patent No.

5,736,928, assigned to the assignee hereof, entitled Pre-Processor Apparatus and Method and incorporated herein by reference. Three sample processing, so- called min-three processing is described and illustrated therein.

The processed outputs on line 50a could in addition be coupled to the comparators 54a, b. It will be understood that the comparators 54a, b could be implemented in hardware or software at the detector 18n. Alternately, that functionality can be provided at common control unit 12.

Where sensor 40 is intended to detect the presence of a fire condition, pre-alarm comparator 54a compares processed sensor output, line 50a to a pre-alarm threshold 54a-1 so as to provide an early indication of the presence of a possible fire condition. In addition, processed sensor output is compared in comparator 54b to an alarm threshold 54b-1 which is indicative of the presence of a substa ntial enough indication of a fire that an alarm, which could be given via members of the plurality 26, should be provided. It will be understood that other variations are possible beyond the pre-alarm threshold and alarm threshold illustrated in Fig. 2, all without departing from the spirit and scope of the present invention.

Since the profile detection circuitry 42 is intended to address a developing ambient condition, various analysis approaches can be implemented.

One profile can be based on a rate of change of sensor output signals. For - example, circuitry 42 can detect the presence of increasing amplitude values on the line 40a. This rate can be compared to a preset rate. Where amplitude values on the line 40a assume a random distribution, no profile of interest is present. Hence, a relatively long quiescent sample interval, on the order of six seconds can be established.

In the event that the signal on the line 40a exhibits increasing amplitude for three successive sample values, the sample interval can be reduced from six seconds to two seconds irrespective of the amplitude value on the line 40a. Siniffarly, if desired, if the amplitude increases for four successive samples, the sampling interval can be decreased from 2 second intervals to one second intervals. As a result, the processing circuits 50 will receive samples at a substantially higher rate. These samples will then be analyzed either at the detector l8n or at the common control unit 12 to determine the presence of an alarm condition.

It will be understood that other types of profile detection can be used without departing from the spirit and scope of the present invention. For example, the sensor output signal can be integrated over time or averaged to create a profile.

Fig. 3 includes a graph which illustrates the above processing where the profile detector 42 responds to three successive increasing amplitude values on the line 40a. As illustrated in Fig. 3, where the output on line 40a from sensor 40 exhibits random values, in a two second through 20 second time period, a quiescent sample rate having six second intervals is used. At 26 seconds, a preliminary potential fire profile is detected by circuitry 42 in response to detecting three increasing amplitude values in a row. At 26 seconds, the profile detection circuitry 42 causes the sampling rate determination circuitry 46 to switch from a six second interval to a two second interval.

51a illustrates processed output values on the line 50a on the assumption that the sample rate has not increased. 51b illustrates process sample values on the line 50a in response to a shortened sample interval. The processing circuitry 50, for example, carries out the type of rnih-three processing described in the above identified Tice et al patent that was incorporated by reference.

As illustrated in Fig. 3, as a result of having increased the sample rate at 26 seconds, the processed values on the line 50a, graph 51b, cross the prealarm threshold PRTH sooner than do those of graph 5 la where the sampling rate has not been increased. Similarly, the processed signals on the line 50a cross the alarm threshold ALm sooner than is the case without increasing the sample rate.

Hence, not only do the present apparatus and process result in a lower power requirement, since during quiescent periods the sample rate for the respective detectors is reduced, but they also produce shorter response intervals, due to a higher sample rate when the ambient condition being detected begins to change.

Using a higher sample rate, once a preliminary fire profile has been detected, takes advantage of a greater probability of the presence of an actual fire as reflected by that preliminary profile.

It will be understood that the circuitry 42 through 50 and 54a, b of Fig. 2 could be implemented wholly or in part via a programmed processor 56 (illustrated in phantom) in the detector 18n.

Fig. 4 illustrates an alternate form of a detector 18p in accordance herewith. Detector 18p incorporates first and second ambient condition sensors 60a, 60b. Sensor outputs on respective lines 62a and 62b are coupled to profile detection circuitry 64.

In the detector 18p, the profile detection circuitry utilizes signals on the line 62b to establish the sampling rate for sensor 60a. Circuitry 64 uses samples on the line 62a to establish a sampling rate for sensor 60b.

Profile determination circuitry 64 is in turn coupled to rate determination circuitry 66a, b for the respective sensors, 60a and 60b. Outputs from sensors 60a, b can in turn be coupled to processing circuitry 68, of the type discussed in the above noted Tice et al patent, and then transmitted via interface circuitry 70 to medium 14 or via transceiver 70a, wirelessly, to control unit 12.

For example, profile determination circuitry 64 via rate determination circuitry 66a, b can establish in a clear air or quiescent condition a five or six second sample interval. If, for example, sensor 60a is an optical-type smoke sensor and 60b is an ionization-type smoke sensor, increasing detected levels of smoke represent a potential fire condition. Variable sampling via circuitry 66a, b can be implemented as follows:

if either sensor 60a, or 60b provide an output to the profile determination circuitry 64 which corresponds to a potential fire profile, the sampling rate of both sensors 60a, 60b can -lo- be increased by reducing the sampling interval from on the order of five to six seconds to on the order of two and one half to three seconds - Alternately, if neither sensor produces signals which are indicative of a developing fire profile, circuitry 64 in combination with rate determination circuitry 66a, b will ultimately reduce the sampling rate by increasing the sampling interval to on the order of seven and one-half or eight seconds.

It will be understood that profile detecting circuitry 64 can detect a rate of change of a sensor input to establish the presence of a predetermined profile. Alternately, detection circuitry 64 could implement any other form of a fire profile without departing from the spirit and scope of the present invention.

Figs. 5A-5C illustrate the results of changes in the processing when the sampling rate is increased. This is an example of performance of a smoke detector but it can apply, without limitation, to any other type of ambient condition detector.

The graph of Fig. 5A illustrates processed output:

output(t) = output(t-l).5 + RAW(t).5 when the sampling rate is NOT increased. (RAW(t)is the unprocessed signal from a smoke sensor). The output takes the shape of a step function. The final values reach 550 at 60 seconds.

The graph of Fig. 5B illustrates the output when processed using the above equation except the sampling rate is increased by 5. The output now has higher resolution and takes a better shape indicating a fire profile but still has spikes that are out of profile. The final values reach over 600 at 60 seconds.

The graph of Fig. 5C illustrates the introduction of additional processing (min3) of the processed output when the sampling rate is increased.

The min3 processing removes the spikes from the processed "output" signal that results from the above noted filtering process, A strong fire profile is present in the min3 processed output signal.

The added processing has improved the ability to discriminate a fire from a nuisance when the sampling rate is increased. The values still exceed 550 at 60 seconds, thus not significantly compromising the response time of Fig. 5A.

As illustrated, changing the processing method when the sampling rate is changed can dramatically improve the overall performance.

Changing, of the processing method in conjunction with an altered sampling rate can be as simple as changing the type or degree of filtering or can be implemented by adding new routines where the processing is carried out via software based commands.

From the foregoing, it will be observed that numerous variations and modifications may be effected without departing from the spirit and scope of the invention. It is to be understood that no limitation with respect to the specific apparatus illustrated herein is intended or should be inferred. It is, of course, intended to cover by the appended claims all such modifications as fall within the scope of the claims.

Claims

What is Claimed:

1 An electrical unit comprising:

an ambient condition sensor for generating an output indicative of the sensed condition; a control element coupled to the sensor wherein the element includes circuitry for sampling the output of the sensor at a first rate thereby producing a sampled output, decision circuitry for determining if the sampled output exhibits a predetermined, non-threshold based, profile, and circuitry which in response thereto, increases the sampling rate to a second, higher, rate.

2. A unit as in claim 1 wherein the control element comprises a programmed processor with instructions for increasing the sampling rate from the first rate to the second rate in response to the presence of the profile in the output.

3. A unit as in claim 2 wherein the decision circuitry includes instructions which determine that the profile is present in response to sampled values exhibiting one of an increasing amplitude or a gradient of sampled amplitude values of the output exceeding a selected first value.

4. A unit as in claim 2 wherein the decision circuitry includes a storage unit wherein information defining a predetermined profile is stored therein, and wherein instructions are stored therein for increasing the sampling rate to the second rate in response to the sampled output from the sensor corresponding to the prestored information.

5. A unit as in claim 1 wherein the decision circuitry includes pattern recognition circuitry for determining that the profile is present in the output.

6. A unit as in claim 1 whichAncludes at least a second, different sensor which generates a second output and including interface circuitry coupled to the decision circuitry wherein the profile determination is based, at least in part, on the second output.

7. A unit as in claim 6 wherein the decision circuitry includes circuitry for adjusting the sampling rate of the first output in response to a profile 13 - based, at least in part, on the second output and for adjusting a sampling rate of the second output in response to a profile based, at least in part, on the first output.

8. A unit as in claim 6 wherein the ambient condition sensor includes a smoke sensor and the second sensor includes a sensor selected from a class which includes a smoke sensor, a gas sensor, a humidity sensor, a thermal sensor, a dust sensor and a velocity sensor.

9. A unit as in claim 7 wherein the decision circuitry comprises a programmable processor and a plurality of associated decision-related instructions coupled thereto, and, wherein the sampling rate adjusting circuitry comprises rate modifying instructions coupled to the processor.

10. A unit as in claim I which includes circuitry for processing the sampled output to thereby produce a processed output wherein the processing is alterable in response to increasing the sampling rate.

11. A unit as in claim 10 wherein the processing comprises filtering the sampled output and wherein the filtering is altered in response to increasing the sampling rate.

12. A processing method in accordance with claim 8 comprising:

sensing a first ambient condition and generating a first output; sensing a second ambient condition and generating a second output; establishing a first sampling rate for the first output; and modifying the sampling rate for the first output in response to the second output.

13. A method as in claim 12 which incudes:

establishing an initial sampling rate for the second output; and modifying the sampling rate for the second output in response to the first output.

14. A method as in claim 12 wherein the modifying step includes analyzing the second output to determine if a selected pattern is present therein.

15. A method as in claim 13 wherein the second output modifying step includes analyzing the first output to determine if a selected pattern is present therein.